I am new to LightBurn and have watched several How-To videos on YouTube. My question is how do you figure out the depth of a cut. Example: One YT-er says to set the cut depth to 1/8 inch and shows settings she uses. Is this just done by trial and error?
Obviously, laser strength and speed effect depth of cut but I was just wondering if there were guidelines posted somewhere.
It depends on the materialā¦Just increase until it cuts through ok, and I add one more for material inconsistency.
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Hey Roger, thanks for asking about this. Controlling āDepth of Cutā with a laser is not something commonly done. You can do it, but yes, trial and error. Each laser system has slight variances to consider, along with the material you plan to use.
Tell us more about the project you are working, we are interested and may have helpful suggestions for ways to accomplish your goal. 
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It was something I saw on a YouTube video. The figure was cut to aprox 1/8 inch depth and then colored epoxy poured into the engraving. Looked like a fun project.
This is the link if you are interested: https://www.youtube.com/watch?v=nlIJrKc6IJM&t=36s
For what you are trying to do, you need to run a material test (found under the Laser Tools menu) changing values until you find the result you are after. Running a material test will become your new best friend.
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That is kinda what I figured. I just wondered if there were Rules of Thumb somewhere. Thanks.
It exists, but individually for each machine.
I āknowā, my machine will cut e.g. 3mm MDF at approx. 25mm/s with 35% powerā¦, so my material test, which I use for all materials and thicknesses, will have a range from 15mm/s to 35mm/s and 20% to 50% (approx.) With an interval of 5 I will very quickly reach the correct parameters. That is the experience value, which is (my) rule of thumb.
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Obviously it depends on the material to be used. In my opinion, cutting depth will always be approximate and inconsistent.
However, I dare say that I have already tested the depth on sponge using the āmaterial testā tool in āfillā mode.
The smell, smoke and risk of fire were very obvious, but I was able to test the depth easily.
It is very easy to do this on sponge because it is easy to cut with the laser.
Another experiment I did, in this case on K-line, was to draw several lines, for example with 20mm, but when doing the test I only placed the material at 15mm of cutting.
In other words (trying to make myself understood) the material only occupies 15mm of the 20mm path of the laser.
This way I was able to evaluate, looking in to material edge, the settings needed to cut just a little more than half the thickness of the material. (My machine does not cut the K-line efficiently from one side to the other).
I hope I have helped in some way. 
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Over cutting is a good idea. If I am concerned with the overrun, butting a waste piece of wood would absorb the overrun. Thanks. Good idea.
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If you happen to be doing an array of pieces such as keyrings and your relying on the experience of usually using five passes itās horrible to find that a particular piece/area of material needs six passesā¦somtimes its a very small uncut that does it.
I started cutting clean at five passes for 5mm birch ply and Im up to nine passes now, on the third 8x4ft sheet. This one āfrom the same supplierā has void pockets, nylon fibre and is resulting in Time loss and material waste as well as pre laser treatments to the wood that may effect cutting efficiency.
If Iām doing a double sided keyring where I mirror the piece and swap to lase the reverse side of each, its a nightmare to have a non-totally clean cut āOk, I should have a jig by now, butā¦ā.
Anyway, the material quality will be improving soon and the extra cutting pass or two! does make for less troublesome making.